1. Field of the Invention
The present invention relates to surface modified organic black pigments, surface modified carbon blacks, pigment mixtures using them, and low dielectric black dispersions, coatings, films, and black matrices containing them. The present invention also relates to color filter on arrays having these black matrices, and liquid crystal devices including these color filter on arrays. The present invention further relates to methods of preparing and making these various materials.
2. Description of the Related Art
Electric display devices convert electric information into images. Display devices, such as a liquid crystal display (LCD) device, an electrophoretic image display (EPID), and the like, display an image using optical properties, such as reflection, scattering, interference, and so forth. One conventional LCD device is a thin film transistor liquid crystal display (TFT-LCD). A conventional TFT-LCD has included a thin film transistor (TFT) array substrate, a color filter substrate, and a liquid crystal layer sandwiched therebetween. In these prior TFT-LCD devices, the conventional color filters are separated from the color filter glass (i.e., a counter electrode of thin film transistor (TFT) glass where pixels are defined). In these prior TFT-LCD configurations, alignments of color filter RGB pixels perfectly with the original and intended pixels from TFT glass can be problematic, which alignments can significantly reduce the aperture or effective pixel size, and hence can cause leakage of light and gives lower brightness. Color filter on array (COA) technology has been developed in which a COA-TFT substrate of a LCD device is provided to enhance the aperture ratio, and the resolution as well. Some developments in color filter on array technology are shown, for example, in U.S. Pat. Nos. 7,439,090 B2; 7,436,462 B2; and 6,692,983 B1.
Black matrix is a generic name for materials used in color displays to improve the contrast of an image by separating individual color pixels. Black matrixes, for example, have been patterned on a TFT array substrate of a COA-TFT structure to define regions where red, green, and blue filter layers are formed to provide a color filter on the TFT array substrate. The black matrix layer in LCDs has been manufactured by vapor deposition of Cr/CrO. Although chromium based films have excellent light-shielding capabilities, the metal vapor deposition process is expensive. In addition, chromium use and disposal is subject to increasingly restrictive environmental regulations. Chromium films also have low resistivity, which restricts the electrical design of LCDs to a subset of the possible design configurations. An ink jetting process also has been used in the manufacture of a color filter of an LCD. In one form of ink jetting process, a light-shielding layer such as a black matrix has been formed on a glass substrate component of a color filter structure, and the black matrix undergoes exposure and development processing to form a pixel area on the black matrix. Black matrix compositions also have been provided as photocurable compositions, such as photoresistive compositions.
Black pigments such as carbon black have been used in polymer compositions to make resistive black matrices. However, typical systems have not been able to provide the desired balance of overall properties. For example, while a black matrix containing a carbon black pigment could provide the required light-shielding capabilities (that is, an optical density (OD) of greater than 3 at 1 micron thickness), typically the film would have only a modest resistivity. Alternatively, if a highly resistive film were produced, the OD would typically be low.
Modified pigments having attached organic groups have also been disclosed for use in a black matrix for color filters. For example, U.S. Patent Application Publication No. 2003-0129529 A1 relates, in part, to a black matrix prepared using a pigment having attached at least one polymeric group, wherein the polymeric group comprises at least one photopolymerizable group and at least one ionic or ionizable group. Also, U.S. Patent Application Publication No. 2002-0020318 A1 relates, in part, to a black matrix prepared using a pigment having attached at least one organic ionic group and at least one amphiphilic counterion. In addition, U.S. Patent Application Publication No. 2002-0011185 A1 relates, in part, to the use of a pigment having attached at least one alkylene or alkyl group having 50-200 carbons.
However, the design of pigments for black matrices and other uses has been found by the present investigators to be an area having opportunities for advancement beyond prior understandings. The present investigators have recognized, for example, and solved at least in part, a need for materials providing black matrices and dispersions with good overall performance which can exhibit combinations of low dielectric constant, high resistivity, high optical density, and/or high IR transparency properties.